Conventionally, in the field of electronic computers, as their size is reduced and the throughput speed increases, there are increasing demand for magnetic disk apparatuses and other external recording apparatuses wherein they should have higher recording density and higher access speed. Especially in the magnetic disk unit, as the recording density is improved, the recording bit is reduced, and therefore there is a problem in that the output in reproduction by a magnetic head is lowered. For solving this problem, differing from a conventional apparatus using solely one electromagnetic induction type head for use both in recording and reproduction, a recording/reproducing apparatus using a recording head and a reproducing head which are separately provided, namely, using an electromagnetic induction type head for recording and an MR head (magneto-resistive head) for reproduction utilizing a magnetoresistance effect is developed.
The MR heads are roughly classified into AMR (anisotropic magneto-resistance) heads utilizing anisotropic magnetoresistance effect and GMR (giant magneto-resistance) heads utilizing giant magnetoresistance effect. Particularly, the GMR head can realize recording with a density as high as 3 gigabits or more per 1 square inch, and hence the GMR head is mainly used in the field of magnetic disk.
On the other hand, the AMR heads are introduced into magnetic tape cartridge of a single reel type, typically, for example, a DLT (digital linear tape) or LTO (linear tape open format cartridge) and used for reproduction of a recording/reproducing system for magnetic tape. From the technical changes of a hard disk (HD), it is expected that the GMR head will replace the AMR heads in the near future to become the main force in magnetic tape systems.
However, when the GMR head is introduced as a reproducing head in the magnetic tape system, a problem of prevention of ESD (electrostatic discharge) is encountered as a technical issue to be solved.
The ESD prevention is more severe in the GMR head than that in the AMR head, and ESD even at a level that causes no problem in the AMR head can be at a charge level sufficient to break the spin valve element constituting the GMR head. Of course, in the AMR head, the cartridge or magnetic tape may be charged to an excessive amount during a long-term storage or actual use, and the ESD level is required to be lowered from the viewpoint of reliability, although that not constituting a serious problem.
In conventional HD applications, the magnetic head is basically put above the magnetic disk so as not to be directly in contact with the magnetic disk, and the HD is operated only in a grounded housing to satisfactorily ground both the magnetic disk and the magnetic head, thus preventing ESD.
On the other hand, the magnetic tape system is basically removable, and, in jukebox type library using a robotics operation, an action of drawing a cassette is inevitable, and therefore, not only is a possibility of ESD even higher than that of the HD, but also a danger of ESD is considerably high when the use environment is at a low humidity. From this point of view, in the GMR heads in general, or in the AMR heads depending on the actual use environment and time, the high density magnetic recording tape system can in principle have a recording/reproducing density equivalent to that of the HD, but it cannot be satisfactorily realized in the actual application due to the problem of ESD.
In order to solve the above mentioned problems, a method of improving the circuit to prevent ESD is considered as disclosed in Examined Japanese Patent Application Publication No. H07-92718, for example, but it is still not possible to obtain a structure which surely enables drain of electrical charges when the magnetic tape and the head operate both in a moving state. On the other hand, for lowering the electric resistance of a coating type magnetic film, an attempt to add conductive carbon black is made, but, not only does the addition of a nonmagnetic material, which is not a magnetic material, lower the electromagnetic conversion properties, but also the resistance value is roughly controlled, and therefore this is not suitable for control of the performance with high yield.
A medium, such as a tape of a deposited type, has a structure such that the metallic film is inevitably in contact with the MR Head, and hence has in principle a considerably reduced resistance. However, from the viewpoint of the mobility of charges, the electric resistance of the medium is too low, and, when static electricity is generated at a certain point in time, charges move toward the head having the lowest resistance, so that the spin valve element of the GMR head is easily broken.
In view of the above problems, the present invention has been made, and an issue is to provide a magnetic tape cartridge and an apparatus for recording/reproducing the same, which can prevent the magnetic tape from being charged to avoid damage of the magnetic head while lowering the resistance of the magnetic tape and maintaining optimum electromagnetic conversion properties.